At present, with the development of wireless access, there is an increasing demand for throughput and quality of service (QoS, Quality of Service) of a system operating on an unlicensed (Unlicensed) frequency band and a television white space (TVWS, Television White Space) frequency band. One characteristic of the unlicensed frequency band is that a user's right to use a frequency cannot be guaranteed. When a radar or a primary user uses a channel, it is needed to perform a channel switch for the user, and when it is detected that the channel is busy or is used by other users, the user also needs to perform backoff.
In order to guarantee high throughput or high QoS, the system is required to frequently detect channels which are currently available, and then performs a channel switch among multiple channels for a user. In a wireless local access network (WLAN, Wireless Local Access Network) system, when a frequency band on which a basic service set (BSS, Basic Service Set) operates needs a channel switch due to interference or other reasons, an announcement of this channel switch is sent by an access point. A switch command is stored in a channel switch announcement (Channel switch announcement) field and the field is usually sent through being carried in a beacon frame (Beacon). After a channel switch time starts, all users will switch to a new channel for communication.
In the long-term research and development, inventors of the present application found that the channel switch announcement in existing mechanisms is carried in the beacon frame, and although the probability of switch failure for the user may be reduced by transmitting the beacon frame multiple times, the beacon frame has a longer transmission period, and thus is not applicable to a scenario with frequent channel switching.